Atherosclerosis is the leading cause of death in industrialized countries, worldwide. In the United States, myocardial infarctions, almost entirely attributable to coronary artery atherosclerosis, account for 20 to 25% of all deaths. Therapies are available, but no reliable methods can predict in advance which lesions will progress. One major reason is that in situ biopsies of blood vessels is difficult and risky, so histopathology cannot be used routinely to provide information about the state of diseased vessels. A substantial literature of in vitro studies show that fluorescence spectroscopy of arterial walls can distinguish between normal, atherosclerotic and calcified atherosclerotic plaque. Few successful in vivo studies have been done, however, for several reasons. One reason is the lack of a suitable optical probe. Another reason is that hemoglobin absorption often distorts the fluorescence signatures to the point where they cannot be properly analyzed. NLI proposes to address these limitations by designing, fabricating and testing a new side-looking optical probe which will measure, in vivo, both fluorescence and reflectance from arterial tissue. From these two measurements intrinsic fluorescence spectra, undistorted by scattering and absorption processes can be obtained, which will greatly improve the reliability of the optical diagnosis. [unreadable] [unreadable]